High frequency dielectric ceramic composition and fabrication method thereof

ABSTRACT

An improved high frequency dielectric ceramic composition and a fabrication method thereof, which is sintered at a low temperature ranging from 900 DEG  to 1250 DEG  C. without using a sintering aid and which has a fine structure and excellent dielectric characteristics, which includes of TiO2xx(ZnO) where 0.04&lt;/=x&lt;/=1.0.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a high frequency dielectric ceramic composition and a fabrication method thereof, and particularly to an improved high frequency dielectric ceramic composition which is composed of TiO₂ in the amount of 1 mol to ZnO in the amount of 0.04˜1.00 mol.

2. Description of the Conventional Art

Recently, electronic components which are used for a mobile communication device such as a mobile telephone and the like and a receiver/transmitter for satellite communication are made more compact and light. Therefore, the frequency-adaptable parts are generally made in a laminated type or a combined type, with the parts being able to be surface-mounted. A ceramic dielectric material is used for components of an electronic circuit, for example, for a by-pass, coupling, filtering, or the like capacitor, for which, the ceramic dielectric capacitor, due to its temperature compensation characteristic, is particularly used for the fabrication of a coupling circuit, a band filter, a resonator, and the like.

Among important electrical characteristics for fabricating the high frequency devices, there are a high dielectric constant ε_(r) and a low dielectric loss "tan δ", a high quality factor Q, a temperature coefficient of capacitance TCC, and/or of a resonant frequency τ_(f). In addition, a high insulation resistance, a high mechanical strength, a low thermal expansion coefficient, and the like are further desirable for fabricating high frequency devices.

The most important among characteristics for timing and tuning when practically using such the components is the stability of the quality factor, the electrical capacitance, or the resonant frequency. Moreover, for the resonant frequency of a tuning circuit, to be stably maintained, requires a proper measure or a compensation with respect to the circuit environment such as variations in temperature, moisture, voltage, or current.

The conventional high frequency dielectric compositions such as a barium titanate type (BaTi₄ O₉, Ba₂ Ti₉ O₂₀, BaTi₅ O₁₁), a modified magnesium titanate type ((Mg, Ca)TiO₃), a ZST type (Zr, Sn)TiO₄, a barium perovskite (Ba(Zn_(1/3) Nb_(2/3))O₃, Ba(Zn_(1/3) Ta_(2/3))O₃, Ba(Mg_(1/3) Nb_(2/3))O₃, Ba(Mg_(1/3) Ta_(2/3))O₃, a (Ca,Sr,Ba)ZrO₃ type, a (Ca, Sr)((Li, Nb)Ti)O₃, and the like have a sintering temperature ranging from 1300°˜1600° C. With these compositions, it is impossible to fabricate a sintered material having a desired mechanical strength and a dielectric characteristic without adding a sintering aid.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a high frequency dielectric ceramic composition and a fabrication method thereof, which overcomes the problems encountered in the conventional high frequency dielectric ceramic compositions.

It is another object of the present invention to provide an improved high frequency dielectric ceramic composition and a fabrication method thereof having a ternary composition type which is composed of a relatively inexpensive metallic oxide material.

It is another object of the present invention to provide an improved high frequency dielectric ceramic composition and a fabrication method thereof, which is capable of sintering a composition material at a lower temperature ranging from 900°˜1250° C. without using a sintering aid and which has a fine structure and an excellent dielectric characteristic.

To achieve the above objects, there is provided a high frequency dielectric ceramic composition composed TiO₂ ·x(ZnO) where 0.04≦x≦1.0.

To achieve the above objects, there is further provided a high frequency dielectric ceramic composition composed of TiO₂ ·x(ZnO) in which TiO₂ and ZnO are mixed at a ratio of 1:0.04˜1.00 based on their mole %, and are milled by a wet method, calcined, and sintered for 2˜4 hours at 900°˜1250° C.

To achieve the above objects, there is also provided a high frequency dielectric ceramic composition composed of a composition of Zn_(1-y) (Ca,Ba,Sr)_(y) O!_(x) TiO_(3-x), where 0.04≦x≦1.0, and o<y≦0.90, and where a zinc oxide, a titanium dioxide, a calcium carbonate, a barium carbonate, and a strontium carbonate are mixed to satisfy the above-mentioned expression, are milled by a wet method, calcined, and sintered for 2˜4 hours at 900°˜1250° C.

DETAILED DESCRIPTION OF THE INVENTION

The composition according to the present invention is expressed as follows:

    TiO.sub.2 ·x(ZnO)

where 0.04≦x≦1.0

In addition, the composition of the present invention may be composed by partially substituting Zn with more than one element selected from the group composed of Ca, Ba, and Sr, which is expressed as follows:

     Zn.sub.1-y (Ca,Ba,Sr).sub.y O!.sub.x TiO.sub.3-x,

where 0.04≦x≦1.0, and 0<y≦0.90.

The composition of the present invention may be preferably expressed as follows:

     Zn.sub.1-y (Ca,Ba,Sr).sub.y O!.sub.x TiO.sub.3-x,

where 0.5≦x≦1.0, and 0<y≦0.90.

The dielectric ceramic composition according to the present invention can be sintered at a temperature ranging from 900°˜1250° C. The dielectric ceramic composition which is fabricated at the above-mentioned low temperature has a dielectric constant of 18˜53, a quality factor of 1900˜4747 (at 5˜12 GHz), and a temperature coefficient of resonant frequency of -12˜670 ppm/° C.

Namely, since the temperature coefficient of resonant frequency of the composition of TiO₂ ·x(ZnO) (0.04≦x≦1.0) ranges from about +200 to +325 ppm/° C., either CaTiO₃, BaTiO₃, or SrTiO₃ which are matched to TiO2·x(ZnO) in their crystal structures and which have a matrix composition, or a combination of the same to which a proper dielectric compensator is added may be adapted to have a temperature coefficient of 0 ppm/° C. which is required as a temperature characteristic.

The dielectric composition according to the present invention may include one or more than one kind among the above-described compensation dielectrics.

The fabrication method for a dielectric composition according to the present invention is directed to calcining each element composing the composition of the present invention at 900°˜1250° C. Preferably, the composition is sintered at 1100°˜1250° C. for 2˜4 hours.

The dielectric ceramic and the fabrication method thereof according to the present invention will now be explained in more detail with reference to the following examples, however, the scope of the present invention is not limited thereto.

EXAMPLE I

Powders of zinc oxide (ZnO) and titanium dioxide (TiO₂) having a purity of more than 99% were accurately measured. Deionized water was added thereto, and the powder containing the deionized water therein was ground in a wet form by using a zirconia ball for 24 hours. Thereafter, the powder was well dried, and was filtered using a sieve of 100 mesh after mixing a PVA binder-water solution of 2 weight % into the powder. Thereafter, the powder was molded at a pressure of 98Mpa, thus forming a disk-shaped test sample. The thus formed test sample was fired at a heating rate of 300° C./hr for 2 hours at a temperature ranging from 1100° to 1300° C.

The dielectric characteristic of the thusly fabricated ceramic dielectric was measured in the microwave frequency region using an HP-8720C network analyzer. The dielectric constant was measured using a dielectric rod resonator method proposed by Hakki & Coleman, and was obtained by computing the value of the resonant frequency in a TE01 resonant mode. The quality factor and temperature coefficient of resonant frequency were measured in an open transmission cavity. The dielectric constant, the quality factor, and the temperature coefficient in accordance with each sintering are shown in Table I.

                  TABLE I                                                          ______________________________________                                         The microwave dielectric characteristics of a                                  compostion of TiO.sub.2.x(ZnO), where x = 0.04˜1.00.                                                      resonant                                                                               Temp.                                       Sintering Dielectric                                                                               Quality                                                                               frequency                                                                              Temp.                                 x(mol)                                                                               Temp. (°C.)                                                                       constant (εr)                                                                    Factor (Q)                                                                            (GHz)   coeff.                                ______________________________________                                         0.04  1100      --        --     --                                                  1200      59        920    6.93    +200                                        1300      57        1740   7.15                                          0.08  1100      79        1950   5.87                                                1200      83        3240   5.83    +310                                        1300      83        3220   5.79                                          0.16  1100      104       700    5.18                                                1200      107       7440   5.51    +305                                        1300      85        2380   5.70                                          0.50  1100      98        3700   5.13                                                1200      102       1650   5.06    +280                                        1300      96        3150   5.26                                          1.00  1100      100       5410   5.17                                                1200      99        4050   5.21    +325                                        1300      97        5020   5.23                                          ______________________________________                                    

The composition of the first example had a dielectric constant of 57˜107, a quality factor of 700˜5400 (at 5.1˜7.2 GHz), and a temperature coefficient of a resonant frequency of +200˜+325ppm/° C.

EXAMPLE II

A dielectric ceramic composition was fabricated using ZnO:TiO₂ =1:1, namely, ZnTiO₃ as the basic constituent, with Zn being substituted with Ca, Ba, and Sr.

In order to substitute an ion of Zn²⁺ in a stoichiometric ZnTiO₃ with ions of Ca²⁺, Ba²⁺, and Sr²⁺, predetermined amounts of zinc oxide, titanium dioxide, calcium carbonate, barium carbonate, and strontium carbonate were added. The detailed amounts of the additives are shown in Table II.

The composition was calcined for 2 hours at 900° C., and was fired for 2 hours at 1100°˜1200° C. The experimental conditions were the same as in Example I except for the above-mentioned conditions. The dielectric characteristics of the dielectric ceramic composition is shown in Table II.

                  TABLE II                                                         ______________________________________                                         The dielectric characteristics of a composition                                of  Zn.sub.1-y (Ca,Ba,Sr).sub.y O!.sub.x TiO.sub.3-x, where x = 1, 0.005       ≦ y ≦ 0.08.                                                                   Sintering                                                                               Dielectric    resonant                                   ele- x       Temp.    constant                                                                              Quality                                                                               frequency                                                                             Temp.                               ment (mol 2) (°C.)                                                                            (εr)                                                                          Factor (Q)                                                                            (GHz)  coe                                 ______________________________________                                         Ca   0.5     1100     25.6   2660   9.15                                                    1150     35.0   3620   9.05                                                    1200     29.2   3180   8.88   +39                                      1.0     1100     25.1   3050   9.18                                                    1150     35.0   3480   9.18                                                    1200     28.6   2950   8.95   +29                                      2.0     1100     24.6   3330   9.69                                                    1150     35.0   3260   9.46                                                    1200     28.3   3470   9.08   +23                                      4.0     1100     23.0   3070   9.85                                                    1150     34.0   3620   9.64                                                    1200     27.9   3400   9.05   +8.7                                     8.0     1100     24.4   2810   9.70                                                    1150     36.0   3060   9.35                                                    1200     29.7   3240   8.84   +22                                 Ba   0.5     1100     24.5   2110   9.82                                                    1150     36.3   1900   9.47                                                    1200     29.4   2600   9.45   +32                                      1.0     1100     25.5   2370   9.79                                                    1150     29.1   2670   9.61                                                    1200     29.1   2140   9.46   +37                                      2.0     1100     24.3   2680   9.69                                                    1150     28.3   2470   9.35                                                    1200     28.5   2930   9.40   +21                                      4.0     1100     27.7   2830   9.47                                                    1150     39.0   1950   9.50                                                    1200     28.3   2600   9.41   +15                                      8.0     1100     24.5   2770   9.83                                                    1150     25.0   2600   9.78                                                    1200     25.4   2930   9.81   -19                                 Sr   0.5     1100     23.0   2940   9.82                                                    1150     28.6   2660   9.44                                                    1200     29.1   2820   9.44   +34                                      1.0     1100     22.9   2740   9.82                                                    1150     28.6   2800   9.40                                                    1200     28.7   2710   9.41   +27                                      2.0     1100     18.5   3210   9.97                                                    1150     28.2   2870   9.59                                                    1200     30.5   2900   9.54   +7.2                                     4.0     1100     22.9   2960   9.84                                                    1150     33.9   3000   9.49                                                    1200     28.4   2120   9.44   -7.4                                     8.0     1100     24.1   2310   9.55                                                    1150     31.2   2400   9.07                                                    1200     31.6   2480   9.16   +47                                 ______________________________________                                    

The dielectric ceramic composition fabricated at a low sintering temperature of 900°˜1250° C. in Example II has an excellent dielectric characteristics with a dielectric constant of 18˜35, a quality factor of 1900˜3600 (at 5˜12 GHz), and a temperature coefficient of resonant frequency of -19˜47ppm/° C.

EXAMPLE III

A dielectric ceramic composition was fabricated using ZnO:TiO₂ =0.5:1, namely, ZnTi₂ O₅, as the basic constituent, with Zn being substituted with Ca, Ba, and Sr.

In order to substitute an ion of Zn²⁺ of a stoichiometric ZnTi₂ O₅ with ions of Ca²⁺, Ba²⁺, Sr²⁺, predetermined amounts of zinc oxide, titanium dioxide, calcium carbonate, barium carbonate, and strontium carbonate were added. The detailed amount of the additives are shown in Table II. In addition, predetermined amounts of calcium carbonate, barium carbonate and strontium carbonate were added. The detailed amounts of these additives are shown in Table III-5. The above-described composition was calcined at 900° C. for 2 hours, and was fired at 1050°˜1200° C. for 4 hours. The other experimental conditions were the same as in Example I in Table I. The dielectric characteristics of the thusly obtained dielectric ceramic composition are shown in Table III-5.

The dielectric composition fabricated at the sintering temperature of 1050°˜1250° C. in Example III had a dielectric constant of 41˜53, a quality factor of 3140˜4740 (at 10˜11 GHz), a Q*f of more than 30,000, and a temperature coefficient of a resonant frequency of -12˜+670ppm/° C., which are excellent dielectric characteristics.

                  TABLE III                                                        ______________________________________                                         The microwave dielectric characteristic of a composition                       of  Zn.sub.1-y Ca.sub.y O!.sub.x TiO.sub.3-x, where x = 0.5, 0.005             ≦ y ≦ 0.50.                                                            Sintering                                                                               Dielectric                                                                              Quality                                                                              resonant                                         y     Temp.    constant Factor                                                                               frequency    Temp.                               (mol 2)                                                                              (°C.)                                                                            (εr)                                                                            (Q)   (GHz)  Q*f.sub.0                                                                            coeff.                              ______________________________________                                         0.5   1050     45.46    3280  10.6099                                                                               34800                                           1100     50.40    3470  10.5800                                                                               36700                                           1150     51.62    4310  10.5119                                                                               45300 +178                                      1200     51.61    4230  10.3279                                                                               43700                                           1250     51.71    4300  10.2659                                                                               44100                                     1.0   1050     45.49    3860  10.5663                                                                               40800                                           1100     50.90    2940  10.5080                                                                               30900                                           1150     50.64    4310  10.5656                                                                               45500 +206                                      1200     51.56    4120  10.4751                                                                               43100                                           1250     51.68    4220  10.1750                                                                               42900                                     2.0   1050     44.29    3670  10.5002                                                                               38500                                           1100     50.80    4300  10.4250                                                                               44800                                           1150     50.80    3730  10.3451                                                                               38600 +188                                      1200     51.34    3990  10.1837                                                                               40600                                           1250     51.21    4160  10.1250                                                                               24100                                     4.0   1050     45.54    270   10.5616                                                                               2850                                            1100     49.90    2980  10.4770                                                                               31200                                           1150     51.62    4220  10.4054                                                                               44000 +202                                      1200     50.14    3710  10.4585                                                                               38800                                           1250     50.03    4660  10.4600                                                                               46700                                     8.0   1050     41.09    260   10.5914                                                                               2750                                            1100     46.80    3390  10.5740                                                                               35800                                           1150     46.97    3800  10.6406                                                                               40400 +148                                      1200     46.81    3910  10.5338                                                                               41200                                           1250     46.95    4200  10.4782                                                                               44000                                     15.0  1100     43.21    3150  10.7421                                                                               33900                                           1150     43.92    3540  10.7966                                                                               38200                                           1200     44.39    3350  10.9468                                                                               36700 +128                                30.0  1100     43.33    3020  10.7592                                                                               32500                                           1150     47.34    2710  10.1235                                                                               27400                                           1200     47.29    2090  10.7654                                                                               22500 +122                                50.0  1100     46.56    2950  10.4194                                                                               30700                                           1150     62.43    1910  9.1697 17500                                           1200     63.62    1620  10.1564                                                                               16500 +205                                ______________________________________                                    

                  TABLE IV                                                         ______________________________________                                         The microwave dielectric characteristic of a composition                       of  Zn.sub.1-y Ba.sub.y O!.sub.x TiO.sub.3-x, where x = 0.5, 0.005             ≦ y ≦ 0.50.                                                            Sintering                                                                               Dielectric                                                                              Quality                                                                              resonant                                         y     Temp.    constant Factor                                                                               frequency    Temp.                               (mol 2)                                                                              (°C.)                                                                            (εr)                                                                            (Q)   (GHz)  Q*f.sub.0                                                                            coeff.                              ______________________________________                                         0.5   1050     51.03    4150  10.3335                                                                               42900                                           1100     52.3     4020  10.4024                                                                               41800                                           1150     50.15    3940  10.5602                                                                               41600 +177                                      1200     51.26    3430  10.3052                                                                               35300                                           1250     52.89    3650  10.1351                                                                               37000                                     1.0   1050     47.95    4240  10.5010                                                                               44500                                           1100     52.10    3970  10.5114                                                                               41700                                           1150     51.30    3830  10.5808                                                                               40500 +227                                      1200     51.21    3860  10.5074                                                                               40600                                           1250     52.48    4330  10.2500                                                                               44400                                     2.0   1050     46.67    3760  10.3576                                                                               38900                                           1100     51.70    4150  10.3136                                                                               42800                                           1150     50.80    4070  10.3357                                                                               42100 +215                                      1200     51.08    3530  10.2031                                                                               36000                                           1250     48.13    4200  10.3215                                                                               43400                                     4.0   1050     45.73    3520  10.5723                                                                               37200                                           1100     50.96    3630  10.4898                                                                               38100                                           1150     49.53    3890  10.6468                                                                               41400 +178                                      1200     49.91    3500  10.4766                                                                               38900                                           1250     49.62    3780  10.4052                                                                               39300                                     8.0   1050     46.61    3140  10.6389                                                                               33400                                           1100     49.60    4100  10.6370                                                                               43600                                           1150     46.96    3790  10.7004                                                                               40600 +138                                      1200     47.15    3070  10.5157                                                                               32300                                           1250     47.24    3140  10.4746                                                                               32900                                     15.0  1100     44.69    3750  10.6732                                                                               40000                                           1150     43.16    1570  10.8090                                                                               12800                                           1200     42.95    2580  10.9491                                                                               28300 +111                                30.0  1100     36.63    1290  11.0750                                                                               14300                                           1150     36.62    1160  11.0540                                                                               12800                                           1200     35.99    910   11.1151                                                                               10100 +24                                 50.0  1100     28.73    2280  11.4304                                                                               26100                                           1150     36.35    3290  11.3311                                                                               37300                                           1200     32.75    3020  11.5677                                                                               34900 -12                                 ______________________________________                                    

                  TABLE V                                                          ______________________________________                                         The microwave dielectric characteristic of a composition                       of  Zn.sub.1-y Sr.sub.y O!.sub.x TiO.sub.3-x, where x = 0.5, 0.005             ≦ y ≦ 0.50.                                                            Sintering                                                                               Dielectric                                                                              Quality                                                                              resonant                                         y     Temp.    constant Factor                                                                               frequency    Temp.                               (mol 2)                                                                              (°C.)                                                                            (εr)                                                                            (Q)   (GHz)  Q*f.sub.0                                                                            coeff.                              ______________________________________                                         0.5   1050     43.56    360   10.6538                                                                               3840                                            1100     48.49    3220  10.6499                                                                               34300                                           1150     50.27    4140  10.6358                                                                               44000 +175                                      1200     50.90    3610  10.6164                                                                               38300                                           1250     50.91    4510  10.3881                                                                               46900                                     1.0   1050     44.94    150   10.5386                                                                               1580                                            1100     50.15    3270  10.6842                                                                               34900                                           1150     51.06    4220  10.5728                                                                               44600 +180                                      1200     51.03    4540  10.5372                                                                               47800                                           1250     46.30    4530  10.5627                                                                               47800                                     2.0   1050     44.40    130   10.5625                                                                               1370                                            1100     48.55    4260  10.6212                                                                               45200                                           1150     50.31    4440  10.6092                                                                               47100 +174                                      1200     50.14    4270  10.6220                                                                               45400                                           1250     50.12    4400  10.3218                                                                               45400                                     4.0   1050     39.22    130   10.6728                                                                               1390                                            1100     46.51    4540  10.6965                                                                               48600                                           1150     48.66    4470  10.6034                                                                               47400 +157                                      1200     48.61    4010  10.5925                                                                               42500                                           1250     51.61    4580  10.2950                                                                               47200                                     8.0   1050     36.25    220   10.8571                                                                               2390                                            1100     45.64    4430  10.9327                                                                               48400                                           1150     46.55    4740  10.7939                                                                               51200 +109                                      1200     46.50    4470  10.7508                                                                               48100                                           1250     48.87    4240  10.4643                                                                               44400                                     15.0  1100     44.00    480   11.0071                                                                               48000                                           1150     44.81    3020  10.7737                                                                               32500                                           1200     44.23    3700  10.9290                                                                               40400 +60                                 30.0  1100     76.45    1050  10.6305                                                                               11200                                           1150     76.84    1070  9.7311 10400                                           1200     77.22    1090  9.4358 10300 +386                                50.0  1100     61.60    2220  9.4743 21000                                           1150     63.46    550   11.6715                                                                               6400                                            1200     135.79   590   11.584 6800  +670                                ______________________________________                                    

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as recited in the accompanying claims. 

What is claimed is:
 1. A high frequency dielectric ceramic composition consisting of TiO₂ ·x(ZnO) wherein 0.04≦x≦1.0, and the composition has a dielectric constant of 18-53 and a quality factor of 1900-4747 at 5-12 GHz.
 2. The composition according to claim 1, wherein said Zn is substituted with a member selected from the group consisting of Ca, Ba and Sr to satisfy the following formula: _(x) TiO_(3-x), wherein 0.04≦x≦1.0, and 0<y≦0.90.
 3. The composition according to claim 2, wherein x is in the range of 0.5≦x≦1.0. 